Synthetic fibers such as polyester or polyamide fibers are used as general-purpose materials in applications such as inner wear or sportswear. However, since these synthetic fibers are hydrophobic fibers, water absorption treatment is required when used in products worn close to the skin in particular, while also having the problem of undergoing a decrease in water absorbency following repeated laundering. The loss of water absorption treatment agent is particularly remarkable when laundering at high temperatures in the manner of so-called industrial laundering used to wash uniforms and the like, thereby resulting in the need for improved washing durability.
Various studies have been conducted on methods for improving water absorbency of polyester.
For example, in Patent Document 1 indicated below, water absorbency is imparted by treating polyester fibers with a wafer absorbing agent followed by covering the water absorbing agent with a hydrogel. In this method, since the water absorbing agent is isparted by processing, deterioration, of water absorbency cannot be avoided even it covered with a hydrogel, performance ends up decreasing following repeated laundering, and there is the potential for performance to decrease even further when subjected to high-temperature laundering in the manner of industrial laundering. Moreover, there is also the risk of impairment of fiber softness as a result of covering the fibers with a hydrogel.
In addition, although Patent Document 2 indicated below describes that a polyester fiber woven fabric is produced by subjecting polyester fibers to alkaline processing followed by treating with a treatment liquid containing a hydrophilic agent, since performance decreases due to repeated laundering in the case of subjecting ordinary polyester fibers to alkaline processing and hydrophilic processing, water absorbency having washing durability cannot be imparted.